In the field of LSIs, the diameter required for silicon single crystals has been increased year after year. At present, silicon single crystals of 6 inches in diameter are used for the latest devices. It is said that in the future silicon single crystals of 10 inches or more in diameter, e.g., silicon single crystals of 12 inches in diameter will be needed.
The silicon single crystal manufacturing methods according to the Czochralski method are classified into two types of conceptions. One type is a method in which a crucible is rotated and the other type is a method in which a crucible is not rotated. At present, all the silicon single crystals according to the CZ method, which are used for LSIs, are manufactured by the method of rotating a crucible and a silicon single crystal in the opposite directions and heating the crucible by an electric resistance heater surrounding the side of the crucible. In spite of many attempts silicon single crystals of over 5 inches in diameter have not been manufactured up to date by any methods in which the crucible is not rotated or by any other heating methods than the above-mentioned one. Nor they will be produced in the future. The reason is that it is impossible to obtain a temperature distribution which is completely concentric with a growing silicon single crystal without the rotation of the crucible and by such heating methods as magnetic induction heating or electric resistance heating from the bottom surface of the crucible. The growth of a silicon single crystal is extremely sensitive to the temperature distribution.
In accordance with the CZ method which rotates the crucible (hereinafter referred to as the ordinary CZ method), a strong convection is caused in the molten silicon owing to the crucible rotation and the electric resistance heater attached to the side of the crucible, and the molten silicon is stired excellently. This is desirable for the growth of a large-diameter silicon single crystal. 1n other words, a complete and uniform concentric temperature distribution of the molten silicon surface is obtained for the silicon single crystal. Therefore, the present invention is based on the ordinary CZ method. As mentioned previously, there is a great difference in molten silicon flow between the ordinary CZ method and the other CZ method. This difference results in considerable variations in the growth of silicon single crystals. As a result, there are great differences between the two with respect to the functions of the furnace components (e.g. the heater). The two methods differ entirely with respect to the conception for the growth of a silicon single crystal.
In accordance with the ordinary CZ method, the amount of molten silicon within the crucible is decreased as a silicon single crystal grows. Thus, as the silicon single crystal grows, the dopant concentration is increased and the oxygen concentration is decreased in the silicon single crystal. In other words, the properties, e.g., the electric resistivity of the silicon single crystal varies in the direction of its growth. Since the quality required for LSIs has been made severer year after year with increase in the level of integration of LSIs, this problem must be overcome.
As a means of solving this problem, there is known a method in which the interior of a quartz crucible according to the ordinary CZ methods is divided by a cylindrical quartz partition member including holes formed therethrough for molten silicon and a cylindrical silicon single crystal is grown on the inner side of the partition member while feeding granular silicon starting material to the outer side of the partition member (e.g., Patent Publication No. 40-10184, page 1, lines 20 to 35).
As pointed out in Laid-Open Patent No. 62-241889 (page 2, lines 12 to 16), this method is disadvantageous in that solidification of the molten silicon tends to occur on the inner side of the partition member with the partition member as a starting point. The cause for this resides in that as will be seen from the fact that quartz is generally used for optical fibers, the quartz forming the partition member excellently conducts heat by radiation. In other words, the heat in the molten silicon is transmitted as light upwardly through the partition member and it is dissipated from the portion of the partition member which is exposed on the molten silicon surface. As a result, the molten silicon temperature is decreased considerably in the vicinity of the partition member. Also, in accordance with the ordinary CZ method, due to the molten silicon being stirred vigorously, the surface temperature of the molten silicon is not only uniform but also just above the solidification temperature. Due to the combination of these factors, the molten silicon surface contacting with the partition member is in a condition having very high tendency to cause the solidification. To avoid this problem, Laid-Open Patent No. 62-241889 proposes a method which uses no partition member. In this method, however, the starting material melting section is so limited that the ganular silicon starting material melting capacity is extremely small and thus it is not put in practical use as yet.
Laid-Open Patent No. 1-153589 is one proposing a method which employs a partition member and prevents the occurrence of solidification thereat. This laid-open patent proposes to completely cover the partition member with a heat shielding member. In accordance with this method, the dissipation of heat from the partition member can be prevented and hence the occurrence of solidification starting at the partition member can be prevented.
However, due to the presence of the heat shielding member between the electric resistance heater and the silicon single crystal, the heat keeping effect of the electric resistance heater on the silicon single crystal is reduced greatly. In other words, the silicon single crystal tends to be cooled. This results in increase in the thermal stresses caused within the silicon single crystal and also the point defects are frozen, thus increasing the micro-defects which are not desirable for the semiconductor and thereby producing a detrimental effect on the growth of the stable silicon single crystal.
The present invention has been made in view of these circumstances and it is an object of the invention to provide a silicon single crystal manufacturing apparatus which is capable of preventing the occurrence of solidification at the meniscus portion (contacting portion of the partition member and molten silicon) of the partition member and properly maintaining the atmosphere temperature of the silicon single crystal during the growing, thereby effecting the growth of the stable silicon single crystal without the occurrence of dislocations.